1. Field of the Invention
The present invention relates to a process wherein certain metals are used in hydroformylation reaction mixtures containing phosphite ligands susceptible to rhodium-catalyzed degradation in order to stabilize the ligands against such degradation.
2. Description of Related Art
It is known to produce aldehydes by hydroformylating reaction mixtures comprising an olefinic compound, hydrogen, carbon monoxide, rhodium and a phosphite ligand. Complex catalysts formed in situ from the rhodium, ligand and carbon monoxide catalyze such hydroformylation reactions. Such processes are disclosed, for example in U.S. Pat. No. 4,599,206 which relates to the use of specific class of phosphite ligands (referred to therein as "diorganophosphite" ligands) in hydroformylation.
Such known hydroformylation processes suffer from the drawback that certain phosphite ligands are susceptible to rhodium-catalyzed decomposition which results not only in a loss of the expensive ligands but which may also result in deactivation of the rhodium by the ligand decomposition products. An example of one type of rhodium-catalyzed phosphite degradation is disclosed in "Synthesis and Properties of the Orthometallated Rhodium Complex Rh{P(OPh).sub.3 }.sub.3 {P(OC.sub.6 H.sub.4)(OPh).sub.2 }", Anna M. Trzeciak and Josef J. Ziolkowski, Z. Anorg. Allg. Chem. 577, (1989), 255-262.
Rhodium-catalyzed phosphite degradation is distinct from acid-catalyzed hydrolytic phosphite degradation disclosed, for example, in "Rates and Mechanisms of Hydrolysis of Esters of Phosphorous Acid", F. H. Westheimer, Shaw Huang, and Frank Covitz, J. Am. Chem. Soc., 1988, 110, 181-185. Phosphites sensitive to one of these forms of degradation may be relatively insensitive to the other form of degradation and stabilizers against one form of phosphite degradation do not necessarily stabilize against the other form of phosphite degradation. For example, published European Patent Application 0590611 discloses that epoxides stabilize phosphites against acid-catalyzed hydrolytic degradation in hydroformylation reaction mixtures but epoxides do not stabilize phosphites against rhodium-catalyzed degradation.
It is an object of the present invention to provide a hydroformylation process using phosphite ligands that are susceptible to, but are stabilized against, rhodium-catalyzed degradation.
Other objects of the present invention will be apparent from the description thereof appearing below.